Add timestamp in the received invocation logs

[hallvictoria]

Description

Added a UTC timestamp to the received invocation logs. Edited tests to check for updated log format.

Fixes #1337

---

PR information

• [ ] The title of the PR is clear and informative.
• [ ] There are a small number of commits, each of which has an informative message. This means that previously merged commits do not appear in the history of the PR. For information on cleaning up the commits in your pull request, see this page.
• [ ] If applicable, the PR references the bug/issue that it fixes in the description.
• [ ] New Unit tests were added for the changes made and CI is passing.

Quality of Code and Contribution Guidelines

• [ ] I have read the contribution guidelines.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (f269c09) 85.81% compared to head (916056b) 85.31%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #1378 +/- ## ========================================== - Coverage 85.81% 85.31% -0.50% ========================================== Files 35 35 Lines 1953 1955 +2 Branches 370 370 ========================================== - Hits 1676 1668 -8 - Misses 208 215 +7 - Partials 69 72 +3 ``` | [Flag](https://app.codecov.io/gh/Azure/azure-functions-python-worker/pull/1378/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Azure) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/Azure/azure-functions-python-worker/pull/1378/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Azure) | `85.26% <100.00%> (-0.50%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Azure#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.